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2008 a Case Study on the Granite Monuments Decay Under Seawater

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2008 a Case Study on the Granite Monuments Decay Under Seawater Berliner Beiträge zur Archäometrie Seite 33-68 2008 A case study on the granite monuments decay under seawater. The reco­ vered relics in Alexandria - Egypt. T AREK NAZEL AND JOSEF R IEDERER Rathgen research laboratory, Berlin, Germany. Abstract: The deterioration of granite monuments under seawater has been studied on fo urteen granite arti facts from more than thirty - six relics from variable materia ls were reco­ vered from the sea, some of them was ex hibited and some was stored in the open Roman theater, in the national museum of Alexandria, in the marine museum and in the Egyptian museum. The study concerns with the determination of some petrophy­ sical, mineralogical. chemical and petrographic characteristics of both weath ered samples from the studied recovered artifacts and fresh from Aswan quarries from where the stone of these artifacts was extracted to allow having a sight into the hi sto­ ry of the g ranite stone o f arti facts before cxtracting and being as a monument and also before exposing to the new circumstances under seawater. XRD, XRF and pola ri zed mi croscope were used for the determinati on ofthe last three mentioned characteri stics of samples respectively. All these analyses and investigati ons aim to find which deterioration causes and pro­ cesses acted in the granite artifacts under seawater in relation to study of the marine environment in Alexandria and the human impact on it as a comparison with the quar­ ries g ranite. Two main kinds of deterioration morphology were found affecting the recovered arti­ facts, thc First conccrns with thc aesthetic va lues of the monuments and this includes the attachment of cerals with the artifacts surfaces (fig.l) and the metal corrosion stains whi ch were produced from the contact with metals or organic materials under seawater for a long time (fig.2), the secend kind of deteri oration morphology refl ects the sevcre state o f cleterioration which the artifacts sutfer from. Four granite decay fo rms were found in our case beleng to th is kind of morphology, these are: I) The superficial detachments and this includes three different names according to the detached layers d imensions: plaques, plaquettes and scales (figures: 3, 4 and 5 respecti ve ly), these different last mentioncd names can be explained according to (8. Silva, et al. , 1996) as follows: plaques occupy a big arca and they are more than 5 mm thick, plaquettes are thinner and scales are thinner and smaller in area, and the last is the commonest decay form in altnost recovered artifacts. 2) Sand disaggregation (fig.6). 33 3) Etch-pitting or (alveolization) (fig.7). 4) Fissuring (fig.8). Figure 1: thc enormous amount of Figure 2: the mctal corrosion stains attached Corals on granite artifact disperse on a part of granite artifact surface. surface. Figure 3: the biggcst dimension of superficial dctachmcnt (plaques). dent view. Figure 5: the smallest form of su­ perficial detachment (thc scale for­ mation). Figure 6: sand disaggregation form. 34 Figure 7: a scvere dcgree of the Figure 8: the fissuring form. etch-pitting form (alveolization) As a result from a statistical study of the decay forms only few cascs were found having the last three mentioned forms of decay as a comparison with the first one. The first kind of deterioration morphology is not serious and unless required for aes­ thetic purposes or to revcal inscriptions there should bc no necd to remove it. As regard to the significance ofthe second kind of morphology as a comparison with the first, the present work studies it and searchcs the causes and processes which Iead to its different forms. Many factors and mechanisms cooperated in sequence long processes to producc the last mentioned granitc decay forms. The first step in these processcs begins in the quarries before the birth of artifact. The abovc mentioned analyses demonstrated that the all studied artifacts suffered from severe physical and chemical alteration in their rock-forming minerals and these were the main serious factors which lcd to the last mentioned decay forms of granite and thc first kind of alteration was the most serious. Twcnty four new formation minerals were detected with XRD analyses as alteration products in the studied samples from the artifacts versus five minerals in the studied samples from thc quarrics. I ntroduction: By the mid fifth century A.D. as the Grcck geographer Stt·abo (Strabo, XVII.) men­ tioned, the most of ancicnt Alexandria was destroycd by a series of earthquakcs and swallowed by the sea. Betwcen 1994-1 998, thc Franco-Egyptian group discovered two main sites of sub­ merged artifacts beneath the watcr ofthe East harbor of Alexandria and not more than 350m distance between them: the first is the site ofthe submerged ruins ofthe famous ancient lighthouse of Alexandria- the Pharos-one ofthe seven wonders ofthe ancient world, more than 2500 artifact were discovercd in an area of more than 25 km' and 35 wait for rai si ng, the second site is the site of the remain s of the submerged Potlemic roya l quarters including the remnants of thc famous fabled palace of Cleopatra, more than 3000 artifacts are believed that scattered along the sea bed from variable shapes and materials. The marine environment of Alexandria was studied, specially the area of thc two archaeological sites. Many environmental problems have grown rapidly in Alexandria in recent decades. thc cnormous growing in population and population density, the urban enlargement and the industrial development are the main reasons ofthese problems, the city affects dramatically its marine environment by discarding all its Iiquid wastes, domestic and industrial into the sea, and by the physical alteration of the coast line by coastal engi­ nccring works. The total cumulative volume of waste water disposcd of into the sea from al l point sources along this stretch of coast is about equal to the Nile outflow from the Rosetta outlet: roughly 9 million mlfday, that is, 3,33 km 1/yr. but th is is not river water. A daily volume of more than one million cubic meters of mixcd scwage watcr is drained from thc city. About one third of this is disposed of without any tre­ atment into the Eastern and Western harbor and their surroundings. Thc Qait Bey outfall (fig.9), located a few hundred meters from the discovcred site of thc lighthouse, releases 200,000 m' ofwaste water pcr day. The East harbor is the reci­ pient of 7 outfalls. This semi-closed harbor rcmains pcrmanently turbid, and water vi ibility is drastically reduced (Y. Halim and F. Abou Shouk, 2000). Mediterrane an Sea 0 5km '""=-=-' Figure 9: The main outfalls: I) Qait Bey and Eastern harbor outfalls: about 200 x IO }.m}.d-' untreated waste water. 2) Lake mariout main basin outfalls about 500 x I O'.ml.d·' primary treated: + 300 x IO'.m' .d·' untreated municipal waste water. 3) Mex pump station on Umoum drain about 7000 x I O'.m}.d ' agricultural drainage water mixed with the overflow from L. Mariout main basin. 4) EI Tabya pump station to Abu Qir Bay: about 2000 x I O'.m'.d·' industrial Waste water. (A fter Y. Hai im and F. Abou Shouk, 2000) 36 Objcctives: Although there are a Iot of archaeological marine sites were discovered in ditferent countries in the world the seawater effect on stone is stilllittle known and there is no attempt was achieved to introduce widely an explanation ofthe decay process ofstone under seawater. Therefore the ultimate scope ofthe work was to understand the decay processes which affect the gran ite monuments under the seawater and also after reco­ vering in order to be in the posi ti on to propose thc appropriate conscrvati on practices specially for granite and generally for the other stones. Materialsand Mcthods: Sampies from two variable varieti es from Aswan granite quan·ies from where the stone of the studied artifacts was extracted were col lected, the first variety is rose coarse granite and thc second is red coarse granite, and they were dcnoted by ASGQ and AOGQ symbols rcspectively. These quarries sampl es were prepared to study in relation to depth, where one core sample of 20 cm long from every variety was cut (accord ing to technique proposed by .1. Delgado et al. , 1996) longitudinally in two hal ves and aft er split in cross thin slabs at I cm interva l. Also samples from fourtecn recovcred granite artifacts were coll ected. Taken into consideration that these artifacts were chosen with sufficient precision to represent the all kinds of thc decay morphologics and also the all varie­ ties of granite. The choose of these artifacts depended on a precise visual observation of more than twenty-seven gran ite recovered objects. The chosen artifacts were divi­ ded according to the decay morphologies whi ch affected by to two groups: I) the first group: includes eleven artifacts affected by The superficial detachments ( cight of them have scale form, two have plaqucttes and one has pl aques), taken into account that this group contains nine arti fac ts belong to Aswan rosc granite variety where this variety is the commonest in the all recovcred artifacts and only two arti ­ facts belong to Aswan red granite variety. Thcy were denoted by symbols SGM (1- 9) and OGM 10 and 11 respectively. 11) the second group: and thi s inc ludes three arti facts, every one of them affected by one of the following decay morphologics: Sand disaggregation, Etch-pitting or (alveolization) and Fissuring, and the three artifacts belong to the rose variety and werc denoted by symbols SGM 12, 13 and 14 respective ly.
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